1. Field of the Invention
This invention relates to a syringe of the type having a fluid-receiving tube provided with an open end and a closed end.
2. Prior Art
Heretofore, it has been proposed to provide a syringe, as in Sausse U.S. Pat. No. 3,696,806, including a fluid-receiving tube having a closed end and an open end, and a resilient plug for relative reciprocating motion in the tube while having relatively firm sealing engagement with the side wall structure of the tube. The plug is connectible to a needle-carrying member which when connected extends through the normally closed plug. The needle-carrying member is operative to hold the plug stationary as the tube is manipulated thereover. It appears that when the tube is in filled condition with the plug occupying the open end of the tube, the holder may be removed from the plug, the resilient plug closing the hole therethrough previously made by the holder. The plug in this position may serve as a tube stopper. The aforementioned extension of the holder through the plug does not appreciably expand the plug as the portion of the holder which extends through the plug is only a thin hollow needle such as a hypodermic needle. The drawback of this article is that the plug sealing pressure on the tube cannot be at least partially relieved which is required, if the plug is to be displaced in the tube as as a function of a specific density thereof greater than one phase of the specimen but less than another phase of the specimen, when the specimen in the tube is centrifuged, not suggested by Sausse.
It has also been proposed, as in Sarstedt U.S. Pat. No. 3,886,928, to provide a fluid-receiving tube closed at one end and open at the other and receiving a needle or cannula holder having as a permanent part thereof an enlargement for relatively firm sealing engagement with the side wall structure with the tube. A granulated material between the enlargement and the bottom of the tube has a specific density intermediate those of a plasma portion and a cell portion of a drawn blood specimen. After such a blood specimen is drawn, the holder may be removed from the tube and the tube placed in a centrifuge to separate the aforementioned portions of the blood specimen. Such separation is effective to place the aforementioned substance of intermediate specific density between such specimen portions as a barrier. However, such barrier has the defect that it does not include a performed plug. While the Sarstedt patent does not disclose a cannula adapter separable from the aforementioned holder and having a valve therein to stop the flow of blood from the donor while the cannula remains injected into a vein in the donor and the holder is disconnected from the adapter, this provision has been made in practice. The provision permits one tube and holder assembly to be exchanged for another with reference to the cannula adapter while the cannula remains injected in the donor for drawing multiple tubes of blood from the donor.
It has also been proposed in an article for collecting blood specimens to provide an evacuated tube having a plug in an open end thereof and having a closed end. According to one aspect of the proposal, a blood specimen is caused to flow through a double-ended needle extended at one end into a vein of the donor and extended at the other end through the plug. After the specimen fills the tube, the needle is removed from both the donor and the plug, and the tube and its contents are subjected to a centrifugal force sufficient to separate the plasma and cell portions of the specimen. Thereafter an additional centrifugal force is applied to displace the plug to a barrier position intermediate the plasma and cell portions, the plug having a specific density intermediate those of the aforementioned specimen portions.
An evacuated blood collection device has the disadvantage that the initial vacuum in the tube may cause the collapse of an injected vein which has reduced elasticity such as caused, for example, by certain types of ill health or advanced age. Evacuated blood collection devices have been known to lose their usefulness as such collection devices by the loss of at least partial vacuum while in storage. Perhaps, the most serious disadvantage of these evacuated devices is that the user does not have any control over the degree of vacuum applied the vein at any time during the collection of a blood specimen. The control is lacking which the user normally has in the use of a conventional syringe, including a piston in a barrel or tube which is manipulated by the user, to create the desired degree of vacuum to draw a blood specimen. The prior art also discloses an alternative technique of filling a tube with a specimen in a manner not requiring the aforementioned evacuated condition of the tube. However, if this technique is used, the tube must be filled from another vessel and the plug is usually positioned in the tube after the filling operation. This manner of use leads to risk of contamination of the specimen and possible loss of identity of the origin of the specimen.
The present invention overcomes these difficulties in prior art specimen collection devices.